1. Field of the Invention
This invention relates to a pump having a decompression device, appropriate for pumping a fluid from a container to an external environment, comprising a jacket defining an inner space, a pumping chamber housed in the inner space of the jacket, and a piston for movement within the inner space of the jacket between an extended position and a retracted position.
2. Description of Related Art
Several variants of this type of pump are known. Movement of the piston modifies the volume of the pumping chamber. On reducing the volume of the pumping chamber, the pressure on the fluid contained therein increases. If this fluid is a liquid, the pressure increases very quickly to high values, and an outlet valve through which the liquid is discharged opens. When the volume of the pumping chamber is increased, a low pressure is generated, causing the outlet valve to close and an inlet valve through which liquid from the container enters is caused to open. Nevertheless, if the fluid contained is a gas, for example air, the pump will generally not work, since the gas is easily compressed and the pressure reached thereby is usually insufficient to open the outlet valve. Therefore, the air is not evacuated. When the volume of the pumping chamber is increased, no depression is created, but rather the internal gas, which is pressurized, expands to reach a final pressure similar to the starting pressure, whereby neither inlet valve nor the outlet valve open. Therefore, the pump requires a purge system allowing this gas to be evacuated.
Pumps of this type usually have a purge system allowing the gas contained in the pumping chamber to be evacuated to the fluid container. This purge system is usually a decompression device which, when the pumping chamber has the smallest volume, i.e., when the pressure of the air contained in the decompression chamber reaches a maximum level, places the pumping chamber in communication with the interior of the container.
This solution, nevertheless, is not desirable when it is desired to pump products that must not be contacted with the air, at least up to the time of use thereof, for example, to avoid drying, oxidation and/or contamination problems.
Containers are known which do not replace the discharged liquid volume with air, but reduce the internal volume of the container, for example, by deformation of the container itself or by movement of a plunger.
It is an object of the invention to provide a pump having a decompression device which may be coupled to one of these containers and which avoids all contact of the liquid with the outside air, until the time of use thereof. This aim is achieved by a pump having a decompression device of the type first mentioned above, comprising a decompression device which, when said piston is in said retracted position, places said pumping chamber in communication with a conduit communicating with said external environment.
Effectively, in this way the air is evacuated from the decompression chamber to a place (the environment external to the pump) where it does not contact the liquid. Generally, this evacuation may take place through any conduit, particularly a conduit in direct communication with the external environment. Nevertheless, a preferred solution is obtained when the pump is provided with a piston comprising a hollow stem defining a communication passage and the conduit is in communication with said communication passage. It should be borne in mind that, when placing the pumping chamber in communication with the conduit, when the piston is in the retracted position, a certain amount of liquid might be discharged through the conduit, since the pumping chamber is pressurized to some extent. Therefore, when the conduit is placed in communication with the communication passage, the possible discharge of the product through an undesired place is avoided, while the conduit is still in communication with the outside, albeit in this case through the communication passage, such that the air may be freely discharged.
The conduit should only be in communication with the pumping chamber when the piston is in the retracted position. This is achieved advantageously by providing the decompression device with a lower lip disposed on the piston and which is interposed between the pumping chamber and the conduit. This lower lip is advantageously resiliently deformed by one or more shoulders disposed in the chamber when the piston is in the retracted position, establishing communication between the pumping chamber and the conduit.
The piston is usually provided with at least one portion which is generally cylindrical, and which defines an outer side surface. The piston slides inside the jacket, which is also provided with at least one generally cylindrical portion and which defines an inner side surface, which faces the outer lateral surface of the piston. There is a certain degree of clearance between the piston and the jacket, allowing an intermediate space, located between both surfaces and between two lips with which the pistons are usually provided to form a tight seal with the jacket, to be defined. A preferred embodiment of the invention is achieved when the conduit is made to communicate with this intermediate space.
Finally, a further advantageous embodiment of the invention is achieved when the piston is provided with a second upper lip, which improves the seal between the pumping chamber and the external environment.